1. Field of the Invention
This invention relates to a new process for the production of salts of 1,3-dioxolane-4-carboxylic acids and to the use of these products as technical and, in particular, as cosmetic humectants.
2. Description of Related Art
1,3-dioxolane-4-carboxylic acids are suitable for use as starting materials for the production of glyceric acid and glyceric acid esters. Because they are not readily available, however, they have hitherto been obtained by acetalization or ketalization of glyceric acid esters. Glyceric acid may be obtained by direct oxidation of glycerin with nitric acid, although the process involved is complicated and gives poor yields.
The acetalization of glycerin with lower aldehydes and the ketalization of glycerin with lower ketones gives a mixture of isomeric cyclic acetals comprising 4-hydroxymethyl-1,3-dioxolanes and 5-hydroxy-1,3-dioxanes which are difficult to separate from one another on account of their similar boiling points (cf. J. Am. Chem. Soc. Vol. 50,(1928), pages 2242-2249 and 3120-3127).
Whereas 5-hydroxy-1,3-dioxane is formed in only small quantities in the formation of cyclic ketals, it is formed in quantities of up to 40% by weight of the isomer mixture in the reaction of glycerin with aldehydes, such as for example formaldehyde and acetaldehyde. The concentration of the 5-hydroxy-1,3-dioxane may continue to increase through gradual spontaneous rearrangement of the 4-hydroxymethyl-1,3-dioxolane, particularly if traces of acid are present. Accordingly, commercial glycerin formal may contain up to 80% by weight of 5-hydroxy-1,3-dioxane.